Jesus prayed that all believers should be one (see John 17) so the world would be convinced that He was all that He claimed to be; and it is very true the differences put people off and so they can claim, “ If you cannot agree, how can we be sure what you say is right and reliable?”
Paul has proved beyond a shadow of doubt in the Book of Romans that the whole of mankind is under condemnation. That is the problem that these doctrines solve. “There is none righteous, no, not one” (Romans 3:10 NKJV). Some might try to argue that they have tried to live a good and honest life, but the Bible tells us that our righteousness, our good works and best efforts are like filthy rags in the sight of God (Isaiah 64:6). We do not possess a righteousness that is acceptable to God.
If that was the end of the matter then we would be left with a very sorry picture indeed; everyone of us on our way to a lost eternity. But Paul is going to show that where there was no way, God made a way.